1. Field of the Invention
This invention relates to electrical switching apparatus such as protective devices and switches used in electric power distribution circuits carrying large currents. More particularly, it relates to such apparatus which uses a large compression spring for closing, and to a modular operating mechanism for mounting and controlling tie storage and discharge of energy in the close spring.
2. Background Information
Electrical switching apparatus for opening and closing electric power circuits typically utilize an energy storage device in the form of one or more large springs to close the contacts of the device into the large currents which can be drawn in such circuits. Such electrical switching apparatus includes power circuit breakers and network protectors which provide protection, and electric switches which are used to energize and deenergize parts of the circuit or to transfer between alternative power sources. These devices also include an open spring or springs which rapidly separate the contacts to interrupt current flowing in the power circuit. As indicated, either or both of the close spring and open spring can be a single spring or multiple springs and should be considered as either even though the singular is hereafter used for convenience. The open spring is charged during closing by the close spring which, therefore, must store sufficient energy to both over come the mechanical and magnetic forces for closing as well as charging the open springs.
Both tension springs and compression springs have been utilized to store sufficient energy to close the contacts and to charge the open spring. The tension springs are easier to control, but the compression springs can store more energy. In either case, a robust operating mechanism is required to mount and control the charging and discharging of the spring. The operating mechanism typically includes a manual handle, and often an electric motor, for charging the close spring. It also includes a latch mechanism for latching the close spring in the charged state, a release mechanism for releasing the stored energy in the close spring, and an arrangement for coupling the released energy into the moving conductor assembly supporting the moving contacts of the switch.
Many operating mechanisms for such electrical switching apparatus utilize side plates for providing partial support for at least some of the operating mechanism components. However, typically, the components are at least partially supported by other parts of the apparatus, such as the housing. For instance, the shafts of the latch and release mechanisms may have one end supported by a side plate, but the other end is supported by the housing. Also, one end of the spring is often supported by other structures. Such arrangements require provision for adjustments to accommodate for tolerances which adds to the cost and complexity of manufacture and assembly of the operating mechanism.
Typically, the force required to charge the close spring increases as the stored energy builds up. This requires the user to apply increased torque during manual charging and necessitates the use of a motor capable of producing the maximum torque needed at the end of the charge cycle. It is known to use a cam in the charging mechanism with a profile which produces a constant charging torque requirement. However, there is no control of the release of the stored energy which can result in contact bounce or contact damage due to excess energy.
Thus, there is room for improvement in electrical switching apparatus of the above types and particularly in the operating mechanism which mounts and controls charge and discharge of the close spring.
Particularly, there is a need for a simple rigid support structure for the operating mechanism of such apparatus which does not require adjustment features for the operating components of the device.
There is a further need for an operating mechanism which controls the release of energy stored in the close spring.
There is another need for such an operating mechanism with an improved arrangement for supporting and controlling the close spring.
There is still another need for such an operating mechanism requiring minimum changes for selectable current ratings, and specifically a simple arrangement for mounting of interchangeable springs.
There is also a need for such an operating mechanism which is a self-supporting modular unit with interchangeable parts.
There is yet another need for such an operating mechanism which is easy and economical to manufacture and assemble.